Preparation, thermoelectric properties and interface analysis of n-type graded material FeSi2/Bi2Te3

Graded n-type β-FeSi2/Bi2Te3 thermoelectric materials have been prepared by dip coating procedure using Sn95Ag5 as bridge material. It was found that an apparent Seebeck coefficient is in between those of β-FeSi2 and Bi2Te3 below 150 °C and higher than both of them between 150 and 300 °C. A measurement shown that the maximum power output of the functionally graded material (FGM) is approximately 2.5–3 times that of monolithic material β-FeSi2 at the same temperature difference, which suggests that not only do the graded material benefit the superior performance of Bi2Te3 from low temperature side, but also make fully use of the properties of β-FeSi2 at high one. Besides, the FGM revealed rather optimistic thermal stability with almost no power output loss even after annealing at 192 °C for 200 h, if a nickel layer was sandwiched between Sn95Ag5 and Bi2Te3 layers. An obvious diffusion of nickel element towards both Sn95Ag5 and Bi2Te3 sides was observed by EMPA, with the former being most likely occurred during long time annealing, and latter being irrelevant to annealing procedure applied.